The mechanism of cell fusion in the single celled green alga Chlamydomonas reinhardi will be studied. The approaches to be used involve experiments that seek to characterize mating structures present on the surface of mating type plus (mt plus) and mt minus gametes. These experiments begin with the preliminary characterization of an enzyme, endolysin which removes the cell wall, allowing access to both the cell surface and mating organelles in each mt. Experiments will be designed to yield isolated preparations of mating structures from wall-less gametes with mt plus mating structures and associated microfilaments. Experiments will be performed to determine the similarity of these filaments to actin, a contractile protein present in higher organisms. These experiments include SDS electrophoresis and autoradiography, immunoelectron microscopy using anti-actin antibody and labeling experiments with meromysin, a protein which binds specifically to actin. The mt minus mating structure will be examined for its component polypeptides by SDS electrophoresis and autoradiography. Proposed experiments will provide information on these polypeptides and the changes they undergo upon activation for cell fusion and following cell fusion. Selected plant lectins will be studied to identify which of the fusion polypeptides present on the mating structure are involved in recognition and/or cell fusion. Experiments will be performed to obtain mutants with a defect in the mt minus mating structure. An analysis of these mutants should provide information on mating structure function and on the mechanism of cell fusion.